The present invention relates to control apparatus for an oil pressure operated transmission in automotive vehicles, inclusive of cars and trucks.
Representative controlling apparatus known in the prior art includes a transmission with at least two stages of low speed and high speed forward driving trains, and it is so arranged that, in an automatic shift range of a manual valve interposed in an oil pressure circuit for the transmission, low speed and high speed oil pressure clutches interposed in the respective forward driving trains may be selectively supplied through a shift valve with pressure oil, and in a hold range of the manual valve, only the low speed oil pressure clutch is supplied with the pressure oil, with the shift valve being kept on its low speed side. This conventional apparatus, however, has such drawbacks that, if the shift valve is locked on its high speed side due to its engagement with dust or the like, the low speed oil pressure clutch cannot be supplied with the pressure oil in both of the automatic shift range and the hold range, resulting in difficulty of starting a vehicle. Further, an engine brake operation and others by using the low speed forward driving train cannot be obtained.
Thus, a need of an apparatus capable of supplying oil pressure to the clutches in all the conditions has long existed in the prior art.
Accordingly, the present invention can be viewed as an effort to fill the need which has long existed for an appropriate control apparatus for oil pressure operated transmission in an automotive vehicle.